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The Nervous System. Functions of the Nervous System. Sensory input—gathering information To monitor changes occurring inside and outside the body Changes = stimuli Integration To process and interpret sensory input and decide if action is needed. Functions of the Nervous System.

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Functions of the nervous system
Functions of the Nervous System

  • Sensory input—gathering information

    • To monitor changes occurring inside and outside the body

    • Changes = stimuli

  • Integration

    • To process and interpret sensory input and decide if action is needed


Functions of the nervous system1
Functions of the Nervous System

  • Motor output

    • A response to integrated stimuli

    • The response activates muscles or glands



Structural classification of the nervous system
Structural Classification of the Nervous System

  • Central nervous system (CNS)

    • Brain

    • Spinal cord

  • Peripheral nervous system (PNS)

    • Nerves outside the brain and spinal cord

      • Spinal nerves

      • Cranial nerves


Functional classification of the peripheral nervous system
Functional Classification of the Peripheral Nervous System

  • Sensory (afferent) division

    • Nerve fibers that carry information to the central nervous system

  • Motor (efferent) division

    • Nerve fibers that carry impulses away from the central nervous system



Functional classification of the peripheral nervous system1
Functional Classification ofthe Peripheral Nervous System

  • Motor (efferent) division (continued)

    • Two subdivisions

      • Somatic nervous system = voluntary

      • Autonomic nervous system = involuntary


Nervous tissue support cells
Nervous Tissue: Support Cells

  • Support cells in the CNS are grouped together as “neuroglia”

  • Function: to support, insulate, and protect neurons


Nervous tissue support cells1
Nervous Tissue: Support Cells

  • Astrocytes

    • Abundant, star-shaped cells

    • Brace neurons

    • Form barrier between capillaries and neurons

    • Control the chemical environment of the brain



Nervous tissue support cells3
Nervous Tissue: Support Cells

  • Microglia

    • Spiderlike phagocytes

    • Dispose of debris



Nervous tissue support cells5
Nervous Tissue: Support Cells

  • Ependymal cells

    • Line cavities of the brain and spinal cord

    • Circulate cerebrospinal fluid



Nervous tissue support cells7
Nervous Tissue: Support Cells

  • Oligodendrocytes

    • Wrap around nerve fibers in the central nervous system

    • Produce myelin sheaths



Nervous tissue support cells9
Nervous Tissue: Support Cells

  • Satellite cells

    • Protect neuron cell bodies

  • Schwann cells

    • Form myelin sheath in the peripheral nervous system



Nervous tissue neurons
Nervous Tissue: Neurons

  • Neurons = nerve cells

    • Cells specialized to transmit messages

    • Major regions of neurons

      • Cell body—nucleus and metabolic center of the cell

      • Processes—fibers that extend from the cell body


Nervous tissue neurons1
Nervous Tissue: Neurons

  • Cell body

    • Nissl substance

      • Specialized rough endoplasmic reticulum

    • Neurofibrils

      • Intermediate cytoskeleton

      • Maintains cell shape



Nervous tissue neurons3
Nervous Tissue: Neurons

  • Cell body

    • Nucleus

    • Large nucleolus

  • Processes outside the cell body

    • Dendrites—conduct impulses toward the cell body

    • Axons—conduct impulses away from the cell body



Nervous tissue neurons5
Nervous Tissue: Neurons

  • Axons end in axonal terminals

  • Axonal terminals contain vesicles with neurotransmitters

  • Axonal terminals are separated from the next neuron by a gap

    • Synaptic cleft—gap between adjacent neurons

    • Synapse—junction between nerves


Nervous tissue neurons6
Nervous Tissue: Neurons

  • Myelin sheath—whitish, fatty material covering axons

  • Schwann cells—produce myelin sheaths in jelly roll–like fashion

  • Nodes of Ranvier—gaps in myelin sheath along the axon



Neuron cell body location
Neuron Cell Body Location

  • Most neuron cell bodies are found in the central nervous system

    • Gray matter—cell bodies and unmyelinated fibers

    • Nuclei—clusters of cell bodies within the white matter of the central nervous system

  • Ganglia—collections of cell bodies outside the central nervous system


Functional classification of neurons
Functional Classification of Neurons

  • Sensory (afferent) neurons

    • Carry impulses from the sensory receptors to the CNS

      • Cutaneous sense organs

      • Proprioceptors—detect stretch or tension

  • Motor (efferent) neurons

    • Carry impulses from the central nervous system to viscera, muscles, or glands



Functional classification of neurons2
Functional Classification of Neurons

  • Interneurons (association neurons)

    • Found in neural pathways in the central nervous system

    • Connect sensory and motor neurons



Structural classification of neurons
Structural Classification of Neurons

  • Multipolar neurons—many extensions from the cell body

Figure 7.8a


Structural classification of neurons1
Structural Classification of Neurons

  • Bipolar neurons—one axon and one dendrite

Figure 7.8b


Structural classification of neurons2
Structural Classification of Neurons

  • Unipolar neurons—have a short single process leaving the cell body

Figure 7.8c


Functional properties of neurons
Functional Properties of Neurons

  • Irritability

    • Ability to respond to stimuli

  • Conductivity

    • Ability to transmit an impulse


Nerve impulses
Nerve Impulses

  • Resting neuron

    • The plasma membrane at rest is polarized

    • Fewer positive ions are inside the cell than outside the cell

  • Depolarization

    • A stimulus depolarizes the neuron’s membrane

    • A depolarized membrane allows sodium (Na+) to flow inside the membrane

  • The exchange of ions initiates an action potential in the neuron


Nerve impulses1
Nerve Impulses

Figure 7.9a–b


Nerve impulses2
Nerve Impulses

  • Action potential

    • If the action potential (nerve impulse) starts, it is propagated over the entire axon

    • Impulses travel faster when fibers have a myelin sheath


Nerve impulses3
Nerve Impulses

Figure 7.9c–d


Nerve impulses4
Nerve Impulses

  • Repolarization

    • Potassium ions rush out of the neuron after sodium ions rush in, which repolarizes the membrane

    • The sodium-potassium pump, using ATP, restores the original configuration


Nerve impulses5
Nerve Impulses

Figure 7.9e–f


Transmission of a signal at synapses
Transmission of a Signal at Synapses

  • Impulses are able to cross the synapse to another nerve

    • Neurotransmitter is released from a nerve’s axon terminal

    • The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter

    • An action potential is started in the dendrite


Transmission of a signal at synapses1

Axonterminal

Actionpotentialarrives

Axon oftransmittingneuron

Vesicles

Synapticcleft

Receivingneuron

Synapse

Transmitting neuron

Neurotrans-mitter bindsto receptoron receivingneuron’smembrane

Vesiclefuses withplasmamembrane

Neurotrans-mitter is re-leased intosynaptic cleft

Neurotransmittermolecules

Synaptic cleft

Ion channels

Receiving neuron

Neurotransmitterbroken downand released

Neurotransmitter

Receptor

Na+

Na+

Ion channel opens

Ion channel closes

Transmission of a Signal at Synapses

Figure 7.10


Transmission of a signal at synapses2

Axonterminal

Actionpotentialarrives

Axon oftransmittingneuron

Vesicles

Synapticcleft

Receivingneuron

Synapse

Transmission of a Signal at Synapses

Figure 7.10, step 1


Transmission of a signal at synapses3

Axonterminal

Axon oftransmittingneuron

Actionpotentialarrives

Vesicles

Synapticcleft

Receivingneuron

Synapse

Transmitting neuron

Vesiclefuses withplasmamembrane

Synaptic cleft

Ion channels

Receiving neuron

Transmission of a Signal at Synapses

Figure 7.10, step 2


Transmission of a signal at synapses4

Axonterminal

Axon oftransmittingneuron

Actionpotentialarrives

Vesicles

Synapticcleft

Receivingneuron

Synapse

Transmitting neuron

Vesiclefuses withplasmamembrane

Neurotrans-mitter is re-leased intosynaptic cleft

Neurotransmittermolecules

Synaptic cleft

Ion channels

Receiving neuron

Transmission of a Signal at Synapses

Figure 7.10, step 3


Transmission of a signal at synapses5

Axonterminal

Axon oftransmittingneuron

Actionpotentialarrives

Vesicles

Synapticcleft

Receivingneuron

Synapse

Transmitting neuron

Neurotrans-mitter bindsto receptoron receivingneuron’smembrane

Vesiclefuses withplasmamembrane

Neurotrans-mitter is re-leased intosynaptic cleft

Neurotransmittermolecules

Synaptic cleft

Ion channels

Receiving neuron

Transmission of a Signal at Synapses

Figure 7.10, step 4


Transmission of a signal at synapses6

Axonterminal

Axon oftransmittingneuron

Actionpotentialarrives

Vesicles

Synapticcleft

Receivingneuron

Synapse

Transmitting neuron

Neurotrans-mitter bindsto receptoron receivingneuron’smembrane

Vesiclefuses withplasmamembrane

Neurotrans-mitter is re-leased intosynaptic cleft

Neurotransmittermolecules

Synaptic cleft

Ion channels

Receiving neuron

Neurotransmitter

Receptor

Na+

Ion channel opens

Transmission of a Signal at Synapses

Figure 7.10, step 5


Transmission of a signal at synapses7

Axonterminal

Axon oftransmittingneuron

Actionpotentialarrives

Vesicles

Synapticcleft

Receivingneuron

Synapse

Transmitting neuron

Neurotrans-mitter bindsto receptoron receivingneuron’smembrane

Vesiclefuses withplasmamembrane

Neurotrans-mitter is re-leased intosynaptic cleft

Neurotransmittermolecules

Synaptic cleft

Ion channels

Receiving neuron

Neurotransmitterbroken downand released

Neurotransmitter

Receptor

Na+

Na+

Ion channel opens

Ion channel closes

Transmission of a Signal at Synapses

Figure 7.10, step 6


Transmission of a signal at synapses8

Axonterminal

Actionpotentialarrives

Axon oftransmittingneuron

Vesicles

Synapticcleft

Receivingneuron

Synapse

Transmitting neuron

Neurotrans-mitter bindsto receptoron receivingneuron’smembrane

Vesiclefuses withplasmamembrane

Neurotrans-mitter is re-leased intosynaptic cleft

Neurotransmittermolecules

Synaptic cleft

Ion channels

Receiving neuron

Neurotransmitterbroken downand released

Neurotransmitter

Receptor

Na+

Na+

Ion channel opens

Ion channel closes

Transmission of a Signal at Synapses

Figure 7.10, step 7


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